The invention is particularly suitable when the gasification proceeds as a partial oxidation of ashy liquid fuels or solid dusty fuels preferably under increased pressure of up to 10 MPa. Liquid fuels here may be ashy heavy oils from the refining of crude oil, or alternatively suspensions of pulverized fuels with water or with liquid hydrocarbons, referred to as slurries. Dusty fuels may be produced from coals in different degrees of coalification, from organic residues or biomasses, optionally after thermal pretreatment.
Reactors employed may be those having a refractory lining or having a cooled reaction chamber surround, as shown in patents DE 4446803 and EP 0677567. A description of the technology is found in J. Carl, P. Fritz “Noell-KONVERSIONSVERFAHREN” [Noell CONVERSION PROCESS], EF-Verlag 1994, sections 2.2 and 2.3, and also in “Die Veredlung and Umwandlung von Kohle” [Refining and Conversion of Coal] DGKM December 2008, M. Schingnitz, section on “GSP Processes”. Undisrupted and continuous deposition of soot and of fine dust formed from slag is vital to reliable operation of catalytically operated processes for the processing of the crude gasification gas to form a synthesis gas that meets the requirements.
A description of the state of the art is given in DE 10 2005 041 930, for example.
Accordingly, the hot crude gas, carrying slag and dust, is transferred from the gasification chamber into a quenching chamber, and is cooled by injection of water to the pressure-dependent saturation temperature. This is about 190-220° C. in the case of an operating pressure of 4 MPa (40 bar), for example. From the quenching chamber, the steam-saturated crude gas and the granulated slag are taken off separately.
Located within the crude gas are particles of soot, of fine slag, of condensed salts introduced with the coal, and dusts in the particle size range of several hundred to <1 μm. They are removed by scrubbing processes to residual levels <1 mg/m3 (STP=standard temperature and pressure). This is done by subjecting the crude gas to intensive water scrubbing in different systems. Use is made, for example, of bubble, jet, and venturi scrubbers, more particularly in that order as well. To remove ultrafine salt mists, which likewise have disruptive consequences for downstream catalytic operations, high pressure water in ultrafine form is sprayed, or the crude gas is cooled slightly to produce a water mist—in both cases with large surface areas—in order to bind even ultrafine components. The crude gas thus cleaned can subsequently be heated further in heat exchangers and supplied, for example, to a catalytic crude gas converting operation for the establishment of the desired H2/CO ratio.
Experience shows that in spite of arranging of a plurality of scrubbing stages operating on different principles, the deposition of ultrafine dust particles or ultrafine drops, in particular, from the spraying of scrubbing water is not achieved completely. Particularly affected is the availability of heat exchangers upstream of the crude gas converting operation, for preheating the crude gas in countercurrent with hot converted gas from the scrubbing temperature, in the region of 190 to 220° C., to the converting temperature, of 270-300° C. As a result of the evaporation of the water on the hot heat exchanger tubes, the ash particles form solid crusts which hinder heat transfer and increase the pressure drops. It has further been found that calcium hydrogencarbonate dissolved in the water is converted into calcium carbonate, incorporates further fine particles, and causes the aforesaid crusting. The reaction equation responsible for this is as follows:Ca(HCO3)2→heat CaCO3+H2O+CO2 